A runner in serious condition last night after collapsing in Sunday's marathon was previously healthy without any medical history, according to a source close to the patient.

The source said the runner, still wheezing and short of breath, was able to speak yesterday but had not fully regained his memory and consciousness.

Chu Man-chung, 33, collapsed near the finish in Wan Chai. He stopped breathing and was resuscitated at the scene before being taken to Ruttonjee Hospital.

Lau Yuk-kong, ardio and intensive care unit consultant at the hospital, refused to comment on individual cases but said patients who had stopped breathing could suffer permanent brain damage.

Dr Lau said even young people without a history of problems could collapse because of hidden heart disease.

Meanwhile a respiratory expert has proposed that people with chronic illnesses should be asked to present medical certificates before being allowed to join marathons after Tsang Kam-yin, 53, died yesterday following his collapse on Sunday.

Chinese University respiratory division head David Hui Shu-cheong said it was safe for runners with complaints such as asthma to race if their condition was under 'good control'.

'But the organiser should take a more proactive approach by reminding runners to be aware of their health conditions and medical history, such as to require those with chronic diseases to present medical certificates from the doctors to prove that they are fit enough to join the event,' Professor Hui said.

Sponsor Standard Chartered said it was grateful for the advice and it would consider all recommendations.

Professor Hui said air pollution, such as that prevailing on Sunday, would cause only minor symptoms in healthy people, including nasal congestion, sore throat and airway irritation. But the pollutants could trigger symptoms more easily among asthma patients.

'The health risk would significantly increase if asthma patients also suffer from other chronic diseases, especially coronary artery disease - the combination can be fatal.'

Professor Hui said it was rare for runners to die just of asthma as they usually stop running as soon as they developed symptoms.